1. Field of the Invention
This invention relates to an image processing apparatus, an information processing method, and an imaging apparatus.
2. Description of the Related Art
A face-image detection technique can be used, for example when viewing a plurality of photographic images captured by a digital still camera, etc. The technique is used for searching a photograph, etc., by extracting face information from each photograph and using the face information as an index to that photograph. Also, the technique is used when adjusting the image quality of a photograph. The image quality is adjusted such that the extracted face area becomes the best one. Furthermore, a face area is detected from an image being captured in real time in order to adjust the camera so that the face area is best exposed or focused. Also, a shooting direction of a camera is controlled by a pan/tilter in order for a face position to be in the center. Moreover, face-image recognition can be applied to a field of security, such as personal identification, etc.
For example, Japanese Unexamined Patent Application Publication No. 20005-44330 describes, in order to determine whether an image in a search window (in the following, referred to as a partial image appropriately) is a face, a method of recognizing a face image, in which a comparison calculation is performed between the pixel values of the partial image and a learning dictionary.
Also, Japanese Unexamined Patent Application Publication No. 2006-48328 describes a face-detection apparatus which allows easy detection of a face area from a shiny image due to the reflected light by glasses, etc.
As described in Japanese Unexamined Patent Application Publication Nos. 2005-44330 and 2006-48328, in a method of detecting a face image, which is applied to a real-time image or stored image data, an image is scanned by a search window to obtain a partial image corresponding to each search window, and whether or not the partial image includes a face is detected. As a method of detecting a face area, for example, comparison processing is performed between the partial image and a template having been obtained by learning in advance. It is possible to use another method of detecting a face area in addition to this. For example, Japanese Unexamined Patent Application Publication No. 2006-48328 describes the following methods. One is a method in which the pixels of a partial image are vectorized and are projected onto a main component space, a distance of the vector to the main component space and the distance of the vector in the main component space are calculated, and a determination is made on whether there is a face area in the partial image. The other is a method in which a face area and an eye-area position are identified from the difference information between a background image (an image not including a human figure) and an image including a human figure.
FIGS. 6A and 6B illustrate one example and another example of scanning for taking out a partial image, respectively. The images shown in FIGS. 6A and 6B are individual examples obtained by acquiring the same object of shooting, but are different in the size of a face. In order to take out a partial image, a search window indicated by a quadrilateral, for example a square is used for scanning, for example from the upper left corner to the lower right corner of the images. The search window is moved its position in the horizontal direction and in the vertical direction by m pixel steps. The m pixels are preferable to be direct proportional to the size of the search window, and are set, for example about one tenth of the length of one side. An appropriate size of the search window is different between relatively large faces shown in FIG. 6A and relatively small faces shown in FIG. 6B. In the case of large faces, the size of the search window becomes large.